Computed tomography scanners (CT scanners) used in the field of dentistry are of the cone-beam type (Cone-Beam Computed Tomography) and comprise an x-ray source-detector assembly designed to rotate about an area of analysis in which the head of a patient is positioned for acquiring volumetric tomographic data of one or both of the dental arches of the patient. The source-detector assembly comprises: a rotating support, constituted typically by a motor-driven arm so as to rotate about a horizontal axis traversing said area of analysis; an x-ray emitter, mounted on a first end of the arm for emitting a conical x-ray beam through the area of analysis; and an x-ray detector, mounted on the opposite end of the arm and facing the emitter for receiving the beam after it has traversed the area of analysis so as to be able to acquire a plurality of radiographies of the dental arches during a single rotation of the arm along an angular path of less than or equal to 360°.
The tomography scanner further comprises a control unit, connected to the source-detector assembly for controlling emission and reception of the beam in a way synchronous with rotation of the arm, and a processing unit, connected to the detector for receiving, storing, and processing the radiographies acquired for different angular positions of the rotating support so as to be able to reconstruct images of dental arches.
The radiation dose that the emitter must emit in order for the detector to be able to acquire a correct radiography depends upon the thickness of the bony parts that the x-ray beam has to traverse, and hence in general upon the dimensions of the skull of the patient. Before acquiring the radiographies, the emitter of the tomography scanner is adjusted for emitting a radiation dose adequate for the skull being examined, for example that of a child or an adult. The radiation dose required is determined via acquisition of one or two radiographies of the patient's head known as scout-views that precedes acquisition of the radiographies for reconstruction of the images.
The tomography scanner of the type mentioned above is hence used successfully for acquiring images of the complete dentition of the patient. In principle, said tomography scanner could be used also for acquiring images of a particular anatomical part located in any point of the patient's head, but the modality of activation of the emitter described above does not enable images of the anatomical part to be obtained having a definition sufficient for the capacities of the average operator.